What Is The Cause Of The Millennial Cycle?

~~Mammo~~ · Jan5-09, 08:02 AM

The 1-2 ky climate cycle is clearly evident in the paleoclimate records and is of primary importance in future predictions. But what actually is the driving mechanism of this cycle?
sciencemag article

**Xnn** · Jan5-09, 11:19 AM

That is a good paper.

In their paper, they argue that a rather substantial change in the North Atlantic's surface circulation brought about a series of ice-rafting events at a frequency of 1470 +- 500 years that was very pronounced during glacial maximum, but since then has occurred as follows:

YrsAgo AD/BC Delta
1400 597 1400
2800 -803 1400
4200 -2203 1400
5900 -3903 1700
8100 -6103 2200
9400 -7403 1300
10300 -8303 900
11100 -9103 800

Notice, the periodicity was poor during the de-glaciation between 11100 to 5900 years ago, but since then became more regular at exactly 1400 years for the last events.

So, by their reckoning we should be just about due for another event. However, with global warming going on as it has, I'd say it doesn't look good for ice rafting in the North Atlantic anytime soon.

**Andre** · Jan5-09, 12:04 PM

Can't assess it but is the Ice rafting supported by ODP-core sediment evidence or is it yet a mere hypothesis?

**Xnn** · Jan5-09, 08:16 PM

I took a closer look at the Science article. Overall, still a good paper, but there are some odd statements buried in there too.

For example, up front they state that the last significant ice-rafting event was 1400 years ago. Since they claim a 1470 year or so cycle, silly me thought that would imply we were due.

Then later on, they state that since the little ice age ended around the the year 1700, it was within +- 500 years of their expected cycle. That is 1100 years after the previous event. However, for some reason they weren't able to present any sediment data for the Little Ice age.

The problem with this is that the little ice age actually began much earlier than 1700 as pack ice began advancing southward starting around 1250. The little ice age is so loosely defined that one could point to any part of 400 year window and since there was no data, it is pure conjecture as to wether or not it was even an event in the first place.
Also, by some reconstructions, the little ice age didn't end until about the year 1750, when the industrial revolution was significantly increasing CO2 emissions.

So, who knows, maybe huge ice burgs would have been showing up off the coast of Ireland if it weren't for greenhouse gases.

**Andre** · Jan6-09, 05:03 AM

Originally Posted by Xnn

Also, by some reconstructions, the little ice age didn't end until about the year 1750, when the industrial revolution was significantly increasing CO2 emissions.

However:

Pre-industrial carbon dioxide levels hovered around 280 ppm until 1850.

Emphazis mine

Better be careful, read the new rule:

Controversial claims must be supported by evidence that comes from a scientific, peer-reviewed journal or a similarly reliable source, i.e., unsubstantiated claims are not allowed.

~~Mammo~~ · Jan6-09, 05:31 AM

It's worth mentioning that the millennial cycle is also found in the cosmogenic isotope data. Wibjorn Karlen therefore believes that the Sun is the source of the cycle (personal communication). Unfortunately no clear millennial cycle is found in the Sun's radiation. The cosmogenic isotope data suggests either an increase in the Solar Wind or a decrease in the Earth's magnetosphere. My personal belief is that it is linked to a cyclical decrease in the Earth's magnetic field and is currently of an unknown cause.

**Xnn** · Jan6-09, 08:47 AM

The thing is we are talking about are ice rafting events off the coast of Ireland.

A lot of things have to come together for that to happen.
Besides being cold enough, the currents have to shift significantly.

Remember, a warm Gulf Current flows from the south towards Ireland/Britain.
All the evidence they found was for iceburgs from Greenland.

So, either the Gulf current would have to shift away and it'd have to be so cold that an iceburg could survive it in for a long time.

My impression is that neither of these happened during the little ice age.

**Xnn** · Jan6-09, 08:53 AM

Andre;

I agree; your claim about CO2 levels hovering until 1850 really needs to be be backed up.

It is overly vague and if you do the research, I'm sure you will find that there
were variations in CO2 levels.

**Skyhunter** · Jan6-09, 01:46 PM

I don't have time to read the paper ATM. But is this ice rafted debris associated with Heinrich events?

**Andre** · Jan6-09, 02:03 PM

Originally Posted by Xnn

Andre;

I agree; your claim about CO2 levels hovering until 1850 really needs to be be backed up.

It is overly vague and if you do the research, I'm sure you will find that there
were variations in CO2 levels.

Click links

Originally Posted by Andre

However:

**Monique** · Jan6-09, 03:40 PM

Xnn, read this post by the administrator: http://www.physicsforums.com/showthread.php?t=280637

It is not clear from what publication the above graph was taken and thus how the data was acquired.

Update:
Since the graph is not directly reproduced from a peer-reviewed source it has been deleted. Please stick to the forum guidelines to maintain a uniform standard of discussion.

**Xnn** · Jan6-09, 08:31 PM

Here is the link to the National Climate Data Center for the Law Dome CO2 record over the past 1000 years:

http://www1.ncdc.noaa.gov/pub/data/p...aw/law_co2.txt

Just put it into Excel.

I used the 75 year smoothed value.

~~Mammo~~ · Jan7-09, 09:16 AM

Originally Posted by Xnn

The thing is we are talking about are ice rafting events off the coast of Ireland.

A lot of things have to come together for that to happen.
Besides being cold enough, the currents have to shift significantly.

Remember, a warm Gulf Current flows from the south towards Ireland/Britain.
All the evidence they found was for iceburgs from Greenland.

So, either the Gulf current would have to shift away and it'd have to be so cold that an iceburg could survive it in for a long time.

My impression is that neither of these happened during the little ice age.

Exactly what is your explanation of Heinrich Events? It is obviously closely linked to the millennial cycle and both need a simultaneous explanation. My best guess is that the Labrador current gains in strength and height due to an increase in the Gulf Stream reaching the Arctic basin.

**Xnn** · Jan7-09, 09:50 AM

Heinrich Events involved the Laurentide ice sheet and occurred relatively infrequently between 7 to 15 thousand years. Since the Laurentide ice sheet is history, we are not about to see any more Heinrich events.

These more modern 1.47K events involved the Greenland ice sheet. The last once occured around the year 597 (according to the paper).

For one to occur again, there would have to be enough ice burgs with cool enough sea temperatures for them to reach the area just east of Ireland.

Correct me if I'm wrong, but the Labrador current flows south westward doesn't it?

So, for an ice burg to get to Ireland, either the gulf current would have to cool, or it would have to shift direction so that ice burgs could travel direct.

**Andre** · Jan7-09, 10:25 AM

Originally Posted by Xnn

Heinrich Events involved the Laurentide ice sheet and occurred relatively infrequently between 7 to 15 thousand years. Since the Laurentide ice sheet is history, we are not about to see any more Heinrich events.

Actually the first Heinrich event occured 60,000 years ago

~~Mammo~~ · Jan8-09, 05:11 AM

Originally Posted by Xnn

Heinrich Events involved the Laurentide ice sheet and occurred relatively infrequently between 7 to 15 thousand years. Since the Laurentide ice sheet is history, we are not about to see any more Heinrich events.

These more modern 1.47K events involved the Greenland ice sheet. The last once occured around the year 597 (according to the paper).

For one to occur again, there would have to be enough ice burgs with cool enough sea temperatures for them to reach the area just east of Ireland.

Correct me if I'm wrong, but the Labrador current flows south westward doesn't it?

So, for an ice burg to get to Ireland, either the gulf current would have to cool, or it would have to shift direction so that ice burgs could travel direct.

The Labrador Current flows south eastward Wikipedia Labrador Current. The idea that I had would be an increase in the strength of this current due to an additional Arctic current during Heinrich Events. The size of the icebergs is also a crucial factor. Perhaps the trans-Atlantic route was not a direct one, but rather a southeast course which is then later picked up by the stronger Gulf Stream and carried northeast.

I also tentatively suggest that the weaker Heinrich Events H3 and H6 Wikipedia Heinrich Events occur during periods of high sea level, which allows the proposed additional Arctic current to overflow through the Bering Strait rather than be primarily channelled down the north Canadian island channels Arctic Map. The average depth of the Bering Strait is only between 30 and 50 meters below current sea level. Wikipedia Bering Strait. This idea seems more applicable to H6 at 60,000 BP, since this is shown to coincide with a sea level just below the land bridge of the Bering Strait. Could this be the reason that there is no evidence of Heinrich Events before 60,000 BP, due to sea levels generally being above 50m? Incidentally, I have just realised that it is even possible that icebergs flowed from the Queen Elizabeth Islands along Greenland's north coast!